Adjustable gastric banding apparatus have provided an effective and substantially less invasive alternative to gastric bypass surgery and other conventional surgical weight loss procedures. Despite the positive outcomes of invasive weight loss procedures, such as gastric bypass surgery, it has been recognized that sustained weight loss can be achieved through a laparoscopically-placed gastric band, for example, the LAP-BAND® (Allergan, Inc., Irvine, Calif.) gastric band or the LAP-BAND AP® (Allergan, Inc., Irvine, Calif.) gastric band. Generally, gastric bands are placed about the cardia, or upper portion, of a patient's stomach forming a stoma that restricts the food's passage into a lower portion of the stomach. When the stoma is of an appropriate size that is restricted by a gastric band, food held in the upper portion of the stomach may provide a feeling of satiety or fullness that discourages overeating. Unlike gastric bypass procedures, gastric band apparatus are reversible and require no permanent modification to the gastrointestinal tract. An example of a gastric banding system is disclosed in Roslin, et al., U.S. Patent Pub. No. 2006/0235448, the entire disclosure of which is incorporated herein by this specific reference.
Over time, a stoma created by a gastric band may need adjustment in order to maintain an appropriate size, which is neither too restrictive nor too passive. Accordingly, prior art gastric band systems provide a subcutaneous fluid access port (“access port”) connected to an expandable or inflatable portion of the gastric band. By adding fluid to or removing fluid from the inflatable portion by means of a hypodermic needle inserted into the access port, the effective size of the gastric band can be adjusted to provide a tighter or looser constriction.
Typically, the access port contains a rubber septum while the rest of the access port (e.g., housing) is constructed out of a hard plastic or metal material. The rubber septum is penetrated by the hypodermic needle to add or remove the fluid. However, after the hypodermic needle is removed, the hole created cannot be allowed to cause a leak. Therefore, the rubber septum should have a self-sealing function and “heal” the hole to prevent a leak after the hypodermic needle is removed.
Certain access ports currently in use are designed to withstand tens to hundreds of punctures by utilizing an interference fit between a cavity defined by two or more mating parts of the access port housing and a rubber septum which is initially larger than the cavity, as illustrated in FIG. 1A. FIG. 1B is a cross-sectional view of another prior art access port, which reveals a fluid reservoir or cavity 130 between a septum 135 and the inside walls of a housing 140. The interference fit 160 between the septum 135 and the access port housing 140 serves two functions: (1) to create a fluid seal at the interface between the septum 135 and the access port housing 140; and (2) to provide compression on the septum 135 which helps to ensure self-sealing after a needle punctures the septum 135. However, one drawback of these access ports is the difficulty in controlling the amount of interference with the rubber septum while concurrently ensuring that the housing parts are effectively assembled together (e.g., either by a press fit or ultrasonic welding, etc.). Because these access port designs rely on the interference created solely by the fit between the septum and the housing, these access ports are forced to use the same rubber durometer to accomplish both the fluid seal function and the self-sealing function. However, using the same rubber durometer for both functions is not optimal because the self-sealing function is more effectively accomplished with a higher durometer rubber (since a harder material more effectively returns to its compressed state under compression), and the fluid seal is better achieved with a lower durometer rubber (since a tighter seal is achieved when the rubber is more easily conformable to the housing). In other words, the use of a higher durometer rubber to promote the septum's self-sealing function compromises the effectiveness of the fluid seal, and conversely, the use of a lower durometer rubber to enhance the fluid seal will limit the septum's ability to self-seal.
What is needed is an access port that allows optimization of the fluid seal function through the use of a better suited rubber material while ensuring that the interference created between the housing and the septum does not adversely affect the self-sealing functionality of the septum.